Recently, a variety of DVD players or DVD recorders have been developed for audio applications or recording media applications. In these DVD players or DVD recorders, systems which can realize speeding-up of the operation speed are desired.
A conventional DVD system will be described with reference to FIG. 6. FIG. 6 is a block diagram illustrating a structure example of the conventional DVD system. As shown in FIG. 6, this system includes a disc interface (disc I/F) 600, a bus control circuit (BCU) 601, a memory 602, an error correcting circuit 603, and a host interface (host I/F) 604.
The data reproduction operation in the DVD system constructed as above will be described with reference to FIG. 6. In the DVD system, first of all, the data 610 from a DVD medium is stored into the memory 602 through the disc I/F 600 and the BCU 601. Next, the data is transferred from the memory 602 to the error correction circuit 603 through the BCU 601. The error correction circuit 603 produces a parity for the data to perform error correction, and writes the error-corrected data into the memory 602. Then, the DVD system transmits the error-corrected data from the memory 602 to the host I/F 604 through the BCU 601.
Next, the data recording operation in the DVD system will be described with reference to FIG. 6. The DVD system initially receives recording data 615 which are transmitted from a host (such as a personal computer or an AV decoder), and stores the data in the memory 602 through the host I/F 604 and the BCU 601. Next, the DVD system transfers the recording data from the memory 602 to the error correction circuit 603 through the BCU 601. The error correction circuit 603 produces a parity for the recording data to perform the error correction, and writes the error-corrected recording data into the memory 602. Then, the DVD system transmits the error-corrected recording data from the memory 602 to a DVD medium through the BCU 601 and the disc I/F 600.
Conventionally, the DVD system implements reproduction of data from a DVD medium and recording of data into a DVD medium in the above-mentioned manners (refer to Patent Document 1), and the data which are recorded in the DVD medium are to be scrambled. Therefore, the data recorded in the DVD medium are the data which have been subjected to a scrambling processing (scrambled data). Therefore, a processing for restoring the scrambled data which are transmitted from the disc I/F 600 into normal data (de-scrambling processing) is required at the reproduction. In contrast, at the recording there is a need to make the data before transmitting the same the disc I/F 600 to the DVD medium subjected to a scrambling processing.
Hereinafter, a scrambling processing according to the DVD scrambling specifications will be described. First of all, ID information which is included in an ID area at the top of the data is converted into an initial scramble seed value (initial scramble SEED value) on the basis of a conversion table shown in FIG. 4. In FIG. 4, the ID information is expressed in a binary number and the initial scramble SEED value is expressed in a hexadecimal number. Further, since a scramble block unit is a sector comprising plural frames under the DVD scrambling specifications, the ID information is included at the top of a sector. The ID information includes information such as a sector number, a layer or a region which the sector belongs to, and the like.
Next, a scramble SEED value is produced from the initial scramble SEED value, as shown in FIG. 5. FIG. 5 is a diagram showing feedback shift registers each storing a scramble SEED value. In the DVD scramble specifications, as shown in FIG. 5, for every 1 bit of main data, an exclusive-OR operation of the 14th-bit and the 10th-bit both of the scramble SEED value is taken and the obtained result is stored in the 0th-bit, and then, the information from the 13th-bit to the 0th-bit are shifted to left, and an exclusive-OR operation and a shift operation are carried out to the amount of the main data, to produce scramble SEED values. Then, scrambling is carried out by taking exclusive-OR operations of the data to be transferred (except for parity) and the scramble SEED values which are produced as described above (refer to Non-patent Document 1). Further, in carrying out de-scrambling, exclusive-OR operations are taken of the scrambled data and the scramble SEED values, thereby de-scrambling the scrambled data.
From the above-described specifications, there are two requirements for the DVD system to carry out scrambling and de-scrambling successfully.
(1) ID Information Includes No Error.
If the ID information includes errors, the initial value of the scramble SEED value (initial scramble SEED value) includes errors and thereby all data will be destroyed by a scramble filter which performs the scrambling process and the de-scrambling process.
(2) Data Address and Address of the Scramble Seed Value Coincide with Each Other.
Since the scramble seed value is different dependent on the position of the scramble SEED value, it is required that the data address and the address of the scramble filter always coincide with each other. If a deviation occurs, the data will be will be destroyed from that address by the scramble filter.
Since there are the above-described two problems, it is general that a scramble filter is inserted in the host interface shown in FIG. 6 in a conventional DVD system. It is because the ID information after the error correction is conducted has a high reliability, continuity of the data is also secured because there are data of all addresses after the error correction, thereby enabling the de-scrambling.    Patent Document 1: Japanese Unexamined Patent Publication No. 11-242647 (FIG. 1)    Non-patent Document 1: ecma international Home Page “DVD format” [searched on Oct. 16, 2003], Ecma-267.pdf